JP3560470B2 - Optical switching element and optical switching element integrated circuit - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical device technology used in fields such as ultra-wideband optical fiber communication and ultra-high-speed optical signal measurement, and relates to an optical switching element and an optical switching element integrated circuit that perform high-speed optical signal processing.
[0002]
[Prior art]
Optical switching of optical control is a technique used in an optical fiber communication system or an optical measurement system using an optical signal in a long wavelength band of 1.3 μm to 1.5 μm. Broadly speaking, there are those that directly use the change in the refractive index of the optical medium due to light, and those that once convert an optical signal into an electric signal and combine the electric signal with a voltage or current driven optical modulator. The latter type, to which the present invention relates, is small in size and excellent in stability, though the number of elements is large.
[0003]
In the case of the latter type using a lithium niobate optical modulator (LN modulator) or a semiconductor electro-absorption optical modulator (EA modulator) as an optical modulator, optical signal switching is performed by optical control as shown in FIG. As shown in the conventional example, the light control signal is converted into an electric signal using the light receiving diode 53, and further, the electric control signal is converted into an electric power level sufficient to drive the modulator using the electric amplifier 62. To amplify. In the prior art, such an optical switching element is configured by combining individual devices. 6, 51 is a bias terminal of the light receiving diode 53, 52-1 is a bias inductor of the light receiving diode 53, 52-2 is a bias capacitance of the light receiving diode 53, 54 and 56 are resistors for bias, and 55 is a DC separation capacitance. Device, 57 is a ground terminal, 58 is an optical modulator, 59 is a bias inductor of the optical modulator 58, 60 is a bias terminal of the optical modulator 58, and 61 is a coaxial cable (50 ohm cable) connecting each device. is there.
[0004]
[Problems to be solved by the invention]
However, such a conventional optical switching element has the following problem. First, the higher the speed of the control signal, the lower the gain of the electric amplifier 62 becomes. Therefore, the complexity of using multiple electric amplifiers 62 and the accompanying increase in power consumption are involved. In addition, since the devices are connected by the coaxial cable 61, signal degradation due to reflection also occurs. Although it is possible to increase the gain of the electric amplifier 62 at the expense of the bandwidth, it is inconsistent with the original purpose of the optical switching element to secure high speed by controlling the optical signal.
[0005]
In addition, the use of the optical NOR logic device requires a large module size and complexity and a problem of signal delay, as long as the conventional technology is assumed. Therefore, there is no proposal or report example.
[0006]
On the other hand, as a switching element for light control in which a light receiving element and a light modulation element are integrated, there is EAS (Excision Absorption Refraction Switch) developed by NTT (C. Amano et al., IEEE Photonics Tech, Lett, 3, 3, 736, 1991). The EARS employs a configuration in which a phototransistor is used as a light receiving element, and the output of the phototransistor drives a multiple quantum well optical modulator. Here, the phototransistor is used because amplification of an electric signal is indispensable for driving the modulator. Since the base terminal of the phototransistor is opened and the amplifying function is provided by a single transistor, it is not suitable for high-speed operation, and can be said to be a light control switching element suitable for miniaturization and array formation.
[0007]
As described above, a high-speed optical control optical switching element applicable to optical communication and the like is merely realized by combining individual light transmission gates with individual devices, and therefore does not include an optical NOR logic device. On the other hand, there is no integrated optical switching element suitable for high-speed operation.
[0008]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and solves problems such as complexity of the device configuration, increase in power consumption, signal degradation, and the like. It is an object to provide a switching element and an optical switching element integrated circuit.
[0009]
[Means for Solving the Problems]
In order to achieve this object, in the present invention, the same optical switching element for converting a plurality of optical input signals composed of time-divisionally ON or OFF signals into a single or a plurality of optical output signals is used. One or more light receiving elements formed on a substrate, one or more light modulating elements, an electric interface circuit for independently biasing the light receiving elements and the light modulating elements, and an input side of the electric interface circuit A first electric wiring connecting both ends of the light receiving element, and a second electric wiring connecting both ends of the light modulation element are provided on an output side of the interface circuit, and one end of the first electric wiring is provided. And the sum of the length of one end of the second electric wiring and the length of one end of the second electric wiring is 1/10 or less of the wavelength of the high-frequency electric signal corresponding to the clock frequency of the input optical signal.
[0010]
Further, the optical output signal is a logical NOR (NOR) value of the plurality of optical input signals.
[0011]
In addition, a single traveling carrier photodiode is used as the light receiving element, and the light modulation element blocks light by inputting an electric signal.
[0012]
An optical logic device comprising a plurality of optical switching elements according to claim 1, 2 or 3, and a plurality of optical waveguides connected between the optical switching elements or the optical switching elements, and performing a logical processing on an optical input signal. An optical switching element integrated circuit having a function is configured.
[0013]
4. The optical branching circuit according to claim 2, wherein the optical logic function has an optical signal dividing function and has two input ports, and a plurality of optical switching elements according to claim 2 or 3 are used. And an optical signal wiring is performed by the optical waveguide.
.
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a block diagram (optical multi-input NOR logic device) showing a basic configuration of an optical switching element of the present invention. As shown in the figure, 1-1,..., 1-n are a plurality of optical input signals composed of time-divisionally ON or OFF signals, and 2-1,. A light receiving element for receiving an input signal; 3, an electric wiring; 5, an optical modulation element; 4, an electric interface circuit intermediate the light receiving elements 2-1,... 2-n and the light modulation element 5; Reference numeral 6 denotes an optical bias (optical control signal) for controlling the optical modulation element 5, and reference numeral 7 denotes a single or a plurality of optical output signals.
[0015]
FIG. 2 is a configuration diagram showing a first embodiment of the optical switching element according to the present invention. As shown in the figure, 13-1 and 13-2 are light receiving diodes as light receiving elements, 14 is an electric interface circuit, and 15 is a light modulation element. 11 is a bias terminal of the light receiving diodes 13-1 and 13-2, 12-1 and 12-2 are bias circuits of the light receiving diodes 13-1 and 13-2 and the light modulation element 15, 16 is a ground terminal, and 17 is light modulation. A bias terminal of the element 15, 18 is an electric wiring, and 19 is a substrate on which element devices are integrated. 20-1 and 20-2 indicate the flow of the optical input signal, 20-3 indicates the flow of the optical bias (optical control signal), and 20-4 indicates the flow of the optical output signal.
[0016]
To operate the present optical switching element, first, when a voltage is applied to the bias terminal 11, the light receiving diodes 13-1 and 13-2 are separated from the light modulation element 15 by the electric interface circuit 14 in a DC manner. Be biased. The bias circuit 12-1 is used to increase the impedance on the bias side as viewed from the light receiving diodes 13-1 and 13-2. Similarly, when a voltage is applied to the bias terminal 17, the light modulation element 15 is separated from the light receiving diodes 13-1 and 13-2 in a DC manner and is DC biased by the electric interface circuit 14. The bias circuit 12-2 is used to increase the impedance on the bias side as viewed from the light modulation element 15.
[0017]
The optical switching operation is performed as follows. When an optical input signal 20-1 or 20-2 enters at least one of the light receiving diodes 13-1 and 13-2, a current is induced, and a voltage change occurs on the optical modulation element 15 side of the electric interface circuit 14. This electric signal is transmitted to the optical modulator element 15, and finally, the light transmittance of the optical modulator 15 is changed by voltage or current driving, and is modulated by the optical bias 20-3 input to the optical modulator 15, and the optical output is changed. It becomes signal 20-4. By selecting the polarity of the electric signal applied to the light modulation element 15, if the light modulation element 15 is arranged to perform an absorption operation when the light control signal is ON, the logical sum of the light input signals 20-1 and 20-2 is obtained. (NOR) value, and “optical NOR logic gate switching” is obtained. Here, two light receiving diodes and one light modulation element are used, but it is also possible to incorporate a plurality of each and perform more complicated signal processing. Further, by changing the configuration of the electric interface circuit 14, the light modulation element 15 can be of a voltage drive type or a current drive type. In addition, if the light modulation element 15 is arranged so as to perform the transmission operation when the light control signal is ON, it is possible in principle to function as "light transmission gate switching".
[0018]
As described above, the optical switching element of the present invention does not use an electric amplifier to obtain an electric signal for driving the light modulation element 15, and instead uses the light receiving diodes 13-1 and 13-2 having a high saturation output. Used. Therefore, the integration is facilitated because the electric amplifier is not integrated. Further, since the number of components is reduced with a simpler element configuration, a small-sized optical switching element with low power consumption can be realized. In terms of element operation, the light receiving diode and the light modulation element can be connected in a lumped-constant circuit with the integration, and the influence of the wiring inductance and the like is reduced. Optical switching can be realized.
[0019]
Further, the length of the electric wiring between the light receiving diodes 13-1 and 13-2 and the light modulation element 15 is set to one of the wavelengths of the high-frequency electric signals corresponding to the clock frequencies of the optical input signals 20-1 and 20-2. / 10 or less and sufficiently shorter than the wavelength of the signal frequency, it is not necessary to send an electric signal to the optical modulation element 15 with a 50Ω line and a 50Ω load, and the load resistance connected to the optical modulation element 15 can be set to an arbitrary value. It is also possible to reduce the resistance value and reduce the CR time constant to increase the speed, or conversely, increase the load resistance value to reduce the required optical input signal power.
[0020]
FIG. 3 is a configuration diagram showing a first embodiment of the optical switching element integrated circuit according to the present invention. FIG. 3A illustrates a set / reset flip-flop circuit and a two-input NOR gate serving as a basic gate thereof. In the figure, 21-1 and 21-2 are optical input signals, 22-1 and 22-2 are optical biases (optical control signals), 23-1 and 23-2 are optical output signals, and 24 is a two-input optical NOR gate. , 25 are optical waveguides, 26-1 and 26-2 are optical bias supply waveguides, and 27 is a substrate. In the two-input optical NOR gate shown in FIG. 3B, reference numerals 28-1 and 28-2 denote input ports, and reference numeral 29 denotes an output port for optical NOR output. The light receiving diodes 13-1 and 13-2 in the optical switching element of FIG. 2 correspond to input ports.
[0021]
From an analogy with an electronic circuit, a set / reset flip-flop can be configured by performing optical wiring as shown in FIG. 3A using the two-input optical NOR gate 24 as a basic unit. Here, an example of a simple set / reset flip-flop has been described, but an optical integrated circuit having other various logic functions can also be configured. Further, FIG. 3B shows the case of a two-input optical NOR gate, but a circuit configuration technique similar to that of an electronic circuit is established with more inputs.
[0022]
FIG. 4 is a configuration diagram showing a second embodiment of the optical switching element according to the present invention. As shown in FIG. 4A, 31 is a bias terminal of a light receiving diode, 32-1 is an inductor, 32-2 is a capacitor, 33-1 and 33-2 are light receiving diodes, 34 is a resistor, and 35 is a DC separation capacitor. , 36 are resistors, 37 is a ground terminal, 38 is a waveguide-type voltage-driven light modulator, 39-1 is an inductor, 39-2 is a capacitor, 40 is a bias terminal of the light modulator, and 41 is a semiconductor substrate. The combination of 32-1 and 32-2 is a so-called bias T, and 39-1 and 39-2 are DC bias circuits. An interface circuit (electric passive circuit) is configured by the resistor 34, the DC separation capacitor 35, and the resistor 36, and the light receiving diodes 33-1 and 33-2 and the light modulation element 38 are DC biased independently by the DC separation capacitor 35. . Also, the bias terminals of the light receiving diodes 33-1 and 33-2 are AC grounded by the capacitor 32-2. By using, for example, InP as the semiconductor substrate 41, the light receiving diodes 33-1 and 33-2 and the light modulating element 38 can be epitaxially grown simultaneously or separately, and monolithic integration is possible. It becomes. In addition, they can be integrated by attaching them to different kinds of substrates by a “wafer bonding method”. FIG. 4B shows an equivalent circuit of FIG.
[0023]
As the light receiving diodes 33-1 and 33-2, for example, a “single traveling carrier photodiode” having a high saturation output recently proposed can be used [T. Ishibashi et al. , Tech. Dig. Ultrafast Electronics and Optoelectronics (OSA Spring Topical Meeting). p. 166 / UWA2-1, 1997]. As the light modulation element 38, for example, an “electroabsorption modulation element” based on the Stark effect of a multiple quantum well can be used [K. Wakita and I. Kotaka, Microwave and Optical Tech. Lett. 7, p. 120, 1994]. The voltage determined by the resistance values of the resistors 34 and 36 is applied to both ends of the light modulation element 38 by the current signals generated by the light receiving diodes 33-1 and 33-2. The optical signal is modulated by this signal, and functions as an optical switching element. Needless to say, by selecting the polarity of the output of the light receiving diode, it can be used as a light transmitting gate.
[0024]
As described above, by using the “single traveling carrier photodiode” having a high saturation output as the light receiving diodes 33-1 and 33-2, the effects of miniaturization and low power consumption are further promoted.
[0025]
FIG. 5 is a configuration diagram showing a second embodiment of the optical switching element integrated circuit according to the present invention. As shown in the figure, in the “optical signal divider” using the optical inverter gate 42-1 and the two-input optical NOR gate 42-2, the two-input optical NOR gate 42-2 is composed of two parallel optical circuits shown in FIG. In the light receiving diodes 33-1 and 33-2, the optical inverter gate 42-1 can be configured by replacing one light receiving diode. The configuration shown in the figure is equivalent to what is called an 8NOR type frequency divider in an electronic circuit, and replaces the electric signal of the electronic circuit with the optical signal intensity, so that the same function can be achieved. Although an example having an optical signal dividing function using an optical branch circuit has been described here, logic circuits having various functions can be configured based on an optical NOR gate.
[0026]
As described in the first and second embodiments of the optical switching element integrated circuit described above, an optical logic circuit can be constituted by using an optical switching element as a basic unit without depending on an electronic circuit. An optical integrated circuit having various optical logic functions such as a flip-flop circuit and a circuit having an optical signal dividing function can be configured. Conventionally, optical logic circuits have been difficult to manufacture on a scale larger than a certain level due to the complexity and inconvenience of being based on laser diodes. In addition, a large-scale integration can be realized stably. In addition, optical logic circuits have advantages that electronic circuits do not have, such as restrictions on impedance matching, restrictions on potential differences between optical circuit chips, and use of parallelism of optical signals. This contributes to the advancement of the system.
[0027]
【The invention's effect】
As described above, in the optical switching element according to the present invention, an optical input signal is converted into an electric signal by the light receiving diode, and the electric signal is input to the optical modulation element to perform the switching operation of the optical bias and other optical signals. Therefore, an electric amplifier is not used to obtain an electric signal required to drive the light modulation element, and a light receiving diode having a high saturation output is used instead. Therefore, the integration is facilitated because the electric amplifier is not integrated. Further, since the number of components is reduced with a simpler element configuration, a small-sized optical switching element with low power consumption can be realized. In addition, with integration, the light receiving unit and the optical modulation unit can be connected as a lumped constant circuit, and the influence of wiring inductance and the like is reduced, so that higher-speed optical switching can be realized without deterioration of the band. . In addition, since the electrical length between the light receiving element and the light modulation element can be sufficiently shorter than the wavelength of the signal frequency, it is not always necessary to send an electric signal to the light modulation element with a 50Ω line and a 50Ω load. Therefore, the load resistance connected to the modulation element can be changed arbitrarily, and the resistance value can be reduced to reduce the CR time constant to increase the speed, or conversely, the load resistance value can be increased to increase the required optical input signal. It is also possible to reduce the power.
[0028]
Further, the optical switching element integrated circuit according to the present invention is based on the optical switching element of the present invention, and can constitute an optical logic circuit without using an electronic circuit. As a result, an optical integrated circuit having various logic functions can be configured. Conventionally, optical logic circuits have been difficult to manufacture on a scale larger than a certain level due to the complexity and inconvenience of being based on laser diodes. In addition, a large-scale integration can be realized stably. In addition, this optical logic circuit has advantages that electronic circuits do not have, such as no restriction on impedance matching, no restriction on the potential difference between optical circuit chips, and the use of parallelism of optical signals. This contributes to the advancement of the system.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a basic configuration of an optical switching element of the present invention.
FIG. 2 is a configuration diagram showing a first embodiment of the optical switching element according to the present invention.
FIG. 3 is a configuration diagram showing a first embodiment of an optical switching element integrated circuit according to the present invention.
FIG. 4 is a configuration diagram showing a second embodiment of the optical switching element according to the present invention.
FIG. 5 is a configuration diagram showing a second embodiment of the optical switching element integrated circuit according to the present invention.
FIG. 6 is a configuration diagram of an optical switching element according to the related art.
[Explanation of symbols]
1-1 to 1-n... Optical input signals 2-1 to 2-n... Light receiving element 3... Electric wiring 4... Electric interface circuit (electric passive circuit)
5 optical modulator 6 optical bias (optical control signal)
7 Optical output signal 11 ... Light receiving diode bias terminal 12-1 ... Light receiving diode bias circuit 12-2 ... Light modulation element bias circuit 13-1, 13-2 ... Light receiving diode 14 ... Electric interface circuit (electric passive circuit) )
15 light modulation element 16 ground terminal 17 light modulation element bias terminal 18 electrical wiring 19 substrates 20-1 and 20-2 light input signal 20-3 light bias (light control signal)
20-4: Optical output signals 21-1, 21-2: Optical input signals 22-1, 22-2: Optical biases 23-1, 23-2: Optical output signals 24: 2-input optical NOR gate 25: Optical waveguide 26-1, 26-2 ... waveguide 27 for supplying optical bias ... substrate 28-1, 28-2 ... input port 29 ... output port 31 for optical NOR output ... bias terminal 32-1 of light receiving diode ... bias of light receiving element Inductor 32-2: Light-receiving element bias capacitances 33-1 and 33-2 Light-receiving diode 34: Resistor 35: DC separation capacitance 36: Resistor 37: Ground terminal 38: Light modulation element 39-1: Light modulation element bias · Inductor 39-2 ··· Bias capacitance 40 of the light modulating element ··· Bias terminal 41 of the light modulating element ··· Semiconductor substrate 42-1 ··· Optical inverter gate 42-2 ··· 2-input optical NOR gate 43 ··· Optical input terminal 4 ... Optical signal divider 45 ... Optical output terminal 46 ... Optical output terminal 51 of the inverted output of 45 ... Light receiving diode bias terminal 52-1 ... Light receiving diode bias inductor 52-2 ... Light receiving diode bias capacitance 53 ... Light receiving diode 54 Resistor 55 DC separation capacitance device 56 Resistor 57 Ground terminal 58 Light modulator 59 Bias inductor 60 Light modulator bias 61 61 Coaxial cable (50 ohm cable)
62 ... Electric amplifier

Claims (5)

In an optical switching element that converts a plurality of optical input signals consisting of time-divided ON or OFF signals into a single or a plurality of optical output signals,
One or more light receiving elements formed on the same substrate,
One or more light modulation elements,
An electrical interface circuit for independently biasing the light receiving element and the light modulation element ,
A first electric wiring connecting both ends of the light receiving element to an input side of the electric interface circuit,
A second electrical wiring connecting both ends of the light modulation element to the output side of the interface circuit,
The sum of the length of one end of the first electric wiring and the length of one end of the second electric wiring is 1/10 or less of the wavelength of the high-frequency electric signal corresponding to the clock frequency of the input optical signal. Characteristic optical switching element. 2. The optical switching device according to claim 1, wherein the optical output signal is a logical NOR (NOR) value of the plurality of optical input signals. 3. The optical switching element according to claim 1, wherein a single traveling carrier photodiode is used as the light receiving element, and the light modulation element blocks light by inputting an electric signal. An optical logic function for logically processing an optical input signal, comprising a plurality of optical switching elements according to claim 1, 2 or 3, and a plurality of optical waveguides connected between the optical switching elements or the optical switching elements. An optical switching element integrated circuit, comprising: The optical logic function has an optical signal dividing function and has two input ports. The optical switching element integrated circuit according to claim 4, wherein an optical signal wiring is provided by the optical waveguide.

Images